1. Field of the Invention
The present invention relates to heat pipes and structures usable therewith which are capable of operating against gravity.
2. Description of the Prior Art
Conventional heat pipes with homogeneous wicks have limited operating capability. Their capability to operate against gravity depends largely on the properties of the working fluid. For example, a heat pipe with Dow-Therm A as the working fluid can operate about two inches in height against gravity, methanol will work up to seven inches, and water can operate up to twenty-four inches. Liquid metal pipes with lithium as the working fluid can operate six to ten feet against gravity; however, the operating temperatures are 1000.degree. C and higher. Even with the best available working fluid, the capability of conventional heat pipes to operate against gravity is limited. Thus, for applications where heat pipes are required to operate ten to forty feet against gravity, their are no single heat pipe systems presently available.
It is possible, of course, to cascade a plurality of heat pipes to overcome the above gravity problems. For example, water heat pipes of two feet in length can be stacked in series to form a forty foot long assembly. One very serious drawback to such a system is that, as the number of stages increase, the overall differential temperature of the system increase. For example, a forty foot long heat pipe, having twenty stages, will gain 2.degree. F per stage for a total of 40.degree. F. Special design can be developed to reduce the overall differential temperature by a judicious design.